Page 94 - Science at the nanoscale

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RPS: PSP0007 - Science-at-Nanoscale
June 12, 2009
From Atoms and Molecules to Nanoscale Materials
84
Schematic to illustrate the difference between (100) and
Figure 4.23.
(111) plane of a NaCl crystal.
Light
diffracted
Incident
in phase
radiation
O
θ
Top plane
d
θ
A
C
Second plane
B
Diffraction of x-ray radiation from periodic planes.
Figure 4.24.
two planes (100) and (110) have very different atomic arrangement ch04
in the NaCl crystal (Fig. 4.23) and hence are rather different in their
chemical behaviours. 10
The structures of crystals are often analyzed by X-ray diffraction
(XRD) technique. When x-ray radiation of wavelength λ passes
through the periodic planes of atoms (Fig. 4.24), the diffraction
angle θ at which constructive interferences are detected is given
10 In these simple cases, crystal planes correspond to layers of atoms, but this is not
generally the case for more complex crystal structures.